The objective of this proposal is to determine the sources of cytotoxic growth inhibitors obtained from the soluble fraction of human dental plaque. At least 3 components which possess this activity can be isolated by column chromatography. These may be bacterially produced, but some or all may be of host origin, having been washed into the plaque with gingival fluid. The inhibitors will be characterized by investigating their modes of action on cells in vitro. By comparing radioactive tracer uptake measurements in inhibitor treated and control cultures, such investigations could pinpoint some enzyme or area of metabolism which is specifically affected by the respective plaque growth inhibitors. Rabbit antisera, made by multiple intradermal injections of the plaque inhibitor preparations in Freunds complete adjuvant will be tested for abolition of inhibitor activity as compared to non-immunized sera. Having obtained these two specific ways of idenifying the plaque inhibitors, extracellular products of Streptococci, Actinomyces, Bacteroides and Fusobacteria, which have been closely associated with existing established gingivitis or severe periodontitis, will be tested for production of toxins. These toxins, or growth inhibitors from macrophages, lymphocytes and other host cells, will be examined for modes of action like those from plaque and also for abolition of their activity by the plaque antiserum. The results of these investigations should provide more information about the respective roles of oral bacteria and the immune response in the production of cytotoxic growth inhibitors in plaque or gingival fluid and hence permit a more direct investigation of their role in periodontal diseases.